Apparatus have heretofore have been made for example as disclosed in U.S. Pat. Nos. 3,453,801; 3,553,059; 3,727,365; 3,729,894 and 3,782,072, for wrapping articles in heat sealable wrapping material as they are advanced along an article path. In the apparatus disclosed in the above mentioned patents, upper and lower webs of heat sealable wrapping material are joined together to form a curtain of material extending crosswise of the article path, and articles are advanced through the curtain to draw the wrapping material along the lead side and along the top and bottom sides of the article. Upper and lower jaw assemblies, supported by upper and lower endless conveyors, are sequentially moved laterally of the article path into positions adjacent the trail side of the article and then forwardly along the article path in clamping engagement with the overlapping webs of material in a sealing run. In the apparatus disclosed in U.S. Pat. Nos. 3,453,801; 3,553,059; 3,727,365 and 3,729,894, the upper jaw assemblies have an electrically energized heat sealing and cutting element mounted thereon to sever the overlapping portions of the web and to seal the overlapping portions of the web at each side of the line of severance. In 3,782,072 the lower jaw assemblies were formed with a pair of clamping jaw members spaced apart in a direction lengthwise of the article path to provide a jaw opening therebetween and a sealing and cutting member was mounted for movement in a closed loop course into the jaw opening in the lower jaw assemblies as they move along a sealing run, to sever and seal overlapping portions of the web at opposite sides of the line of severance, and then out of the lower jaw opening before the upper and lower jaw assemblies reach the end of the sealing run, to allow the sealed webs to cool. Apparatus have also been made in which a cooling member was mounted for movement into and out of the jaw opening in the lower jaw assemblies as they move along the sealing run at a location downstream from the heat sealing and cutting member, to cool the heat sealed joints between the webs.
In the apparatus disclosed in U.S. Pat. No. 3,782,072, the jaw assemblies were spaced apart along the upper and lower conveyors a distance substantially greater then the length of the sealing run, and the jaws are separated at the end of the sealing run to allow the curtain to retract into engagement with the lead side of the next succeeding article. However, at high operating speeds it was found that, in the absence of a succeeding article, the joined webs would frequently not retract fully to the inlet end of the sealing run before the succeeding pair of clamping jaws commenced movement along the sealing run, so that the apparatus continued to seal and sever sections of the joined webs when articles were not advanced through the wrapping machine. This not only wasted wrapping material but also presented the problem of removing of the severed sections of wrapping material from the wrapping apparatus. In addition, in the prior apparatus disclosed in the '072 patent, the sealing and cutting member would continue to cyclically engage the upper clamping jaw when articles were not being wrapped, and this caused additional wear and damage to the upper clamping jaws.
In the apparatus disclosed in U.S. Pat. No. 3,729,894, the heat sealing and clamping jaws are spaced apart along the jaw conveyors a distance less than the length of the sealing run, and provision was made for lowering the guides for the lower jaw assemblies in the absence of an article in advance of the opposed pair of jaw assemblies, to prevent sealing and severing of sections of the webs under these conditions. However, this arrangement wherein the guides for the lower clamping jaws are shifted downwardly in the absence of an article, is not adapted for use in a wrapping apparatus of the type disclosed in U.S. Pat. No. 3,782,072 in which a heat sealing and cutting member is mounted for movement sequentially into and out of a jaw opening in the lower jaw assembly as it moves along the sealing run.